1. Field of the Invention
This invention relates to an apparatus for reproducing still images and, more particularly, to an apparatus for duplicatingly reproducing still images from a signal received from a broadcasting system, for instance.
2. Related Background Art
Recently proposed broadcast television systems intended for practical use, aside from the conventional NTSC system with an aspect ratio of 3:4 and a scanning for instance a HDTV system with an aspect ratio of 9:16 and a scanning line number of 1,125. The HDTV system can deal with about 5 times the image data quantity compared to the NTSC system and also uses a wide screen. Thus, it permits enjoyment of images which are dense and rich in the on-the-spot sense.
However, data quantity has been increased to such an extent that it can not be directly transmitted to each home due to limitations imposed on the broadcast waves and communication capacity. Therefore, bandwidth compression is adopted for transmission on the basis of commonly termed distribution quality, which is slightly inferior to the intrinsic image quality obtained in studio. Table 1 shows an example of specifications concerning the in-studio quality and distribution quality in the HDTV system.
TABLE 1 ______________________________________ In-studio Distribution quality quality ______________________________________ Scanning line number 1,125 1,125 Brightness bandwidth 30 MHz 20 MHz (Y) Brightness sampling 74.25 MHz 48.6 MHz frequency Chromatic difference 15 MHz 7 MHz Bandwidth Chromatic difference 37.125 MHz 16.2 MHz sampling frequency ______________________________________
It is thus inevitable to provide distribution quality for home enjoyment of HDTV system image as motion image.
In the mean time, with the HDTV system the scanning line number is large, and image is dense and less subject to flickering. For this reason, the HDTV system image is enjoyable as still image rather than motion image, and utilization of the HDTV system in the fields of art, culture, education and animation has been expected. In the case of still image, the observer looks at one frame of image thoroughly for several seconds. For this reason, in-studio quality is required as the image quality.
Accordingly, a HDTV still image reproduction apparatus permitting enjoyment of in-studio quality is proposed separately from the HDTV motion image reproduction apparatus. FIG. 2 shows a block diagram of a prior art example of the structure. Reference numeral 10 designates an antenna for intercepting waves transmitted from a broadcasting satellite, 12 a HDTV still image reproduction apparatus, 14 a HDTV color monitor for displaying images with 1,125 scanning lines. In the still image reproduction apparatus, reference numeral 6 designates a tuner for converting waves received by antenna 10 into still image digital compression data, 18 a decoder for decoding still image digital compression data obtained by, for instance, bandwidth compression in a DPCM process, into original image data, 20 an image frame memory for storing one frame of decoded image data from decoder 18, and 22 a D/A converter for converting image data read out from image frame memory 20 into analog signal.
As to the transmission rate, since one still image frame is observed for at least in several seconds, it is usually about 2 Mbps for saving for transmission bandwidth (here bit rate of transmission).
In the prior art system, image data is transmitted unilaterally from the transmission side (for instance from a broadcast satellite). When connecting the power source of the still image reproduction apparatus, an indefinite pattern is displayed on monitor 14 until complete image data of the first frame is stored in image frame memory 20. The indefinite pattern is uncomfortable and is continued for at least several seconds.